Control systems for modern turbine engines measure internal conditions at various positions within the air and the gas flow paths through the turbine engine. Air pressure and temperature measurements may be made through the use of Pitot tubes, thermocouples, and other devices positioned within the compressor and elsewhere. In the absence of suitable hardware, the sensors may be slotted into the compressor or other location on rakes. Rakes are generally mounted onto a machined surface within the compressor and elsewhere.
Currently, compressor inlet volumetric flow measurements are taken using static pressure together with differential pressure measurements in the inlet bellmouth of the turbine engine during continual operation. Compressor inlet mass flow calculation from a volumetric flow measurement additionally requires inlet air density derived from the inlet air temperature and relative humidity measurements combined. This method works reasonably well at full load, where the airflow rate is high and fairly stable, but the accuracy of this approach diminishes as the airflow rate is reduced. Below full speed no load, for example, the current method for measuring airflow is known to be inaccurate and is highly variable. In addition each measurement type has an associated measurement uncertainty, resulting in potentially higher uncertainty than a single measurement. Due to this high variability it is difficult to obtain an accurate understanding of compressor airflow and therefore the utilization of compressor inlet airflow for turbine engine control presents control and diagnostics issues.
Currently, exhaust velocity profiles are measured by utilizing exhaust temperature and total pressure rakes which traverse the exhaust duct. These measurements are then utilized to calculate the exhaust velocity profile utilizing physics based equations. This method works reasonably well for validation testing purposes and is currently applied for the validation of turbine aerodynamic design changes which impact the exhaust flow velocity profile. However, this method requires the installation of two separate sets of rakes increasing the probability of instrument failure during testing. In addition each measurement type has an associated measurement uncertainty, resulting in potentially higher uncertainty than a single measurement. Other than validation testing for the purpose of validating new turbine aerodynamic airfoil shapes the measurement of exhaust velocity and or mass flow profiles is currently not standard within the industry.
Compressor extraction flow measurements for non-modulated turbine engine systems are typically calculated by measuring the temperature and pressure drop across an orifice plate. This method works reasonably well at full load, where the airflow rate through the extraction system is high and fairly stable. However, the accuracy of this method diminishes at lower airflow rates, for which the orifice is over sized, resulting in increased inaccuracy at low loads or low flow levels. In addition the presence of a fixed orifice size in the extraction system limits the functionality of a modulated extraction flow system since at higher flow rates the simple orifice will be the flow limiting component in the extraction flow system.
Accordingly, there is a need for instrumentation for the measurement of exhaust gas velocity profiles to provide a means of validation and calibration of turbine aerodynamic models, and to validate the mixing of exhaust cooling mechanisms. Additionally there is a need for instrumentation for the measurement of turbine engine compressor inlet flow mass flow profiles to enable the validation of the mixing of inlet conditioning measures. There is also a need for instrumentation to accurately measure flow density through a compressor extraction conduit to provide the ability to actively control the level of compressor extraction mass flow rate.